These studies of voice physiology use laryngostroboscopy, with simultaneous signals from Photoglottography (PG(i or transglottal transillumination) and Electroglottography (EGG or trans cervical impedance monitoring) to study the vibration of the vocal folds of humans during voice production, and to study how that vibration is changed with particular variations and abnormalities of muscular tension of the vocal folds. This research will examine how vocal strain, or effortful phonation changes the vibratory patterns of the vocal folds in normal subjects. The work will then compare the effortful phonation of normal voices to measures of vibration in patients who have lost normal voice quality because of vocal nodules, and then will examine how vocal fold vibration changes with successful treatment of the vocal nodules. The research will apply a standard multi-measurement protocol to obtain data during phonation in four populations of subjects with: normal voices, trained voices, and hoarse voices due to vocal nodules. This research addresses an important clinical need to define the pathophysiology of the development of vocal nodules, one of the most common causes of voice loss. This research will also provide important information to be used to develop clinically feasible measures that objectively quantify vocal fold vibration. The long term goals of this work are focused on better diagnoses of voice disorders and better assessment of treatment outcomes.